Enhancement of methanol selectivity in the products of direct selective oxidation of methane in CH4-O2-NO with Cu-ZnO/SiO2 Original Research Article

Enhancement of methanol selectivity in the products of the direct selective oxidation of methane with CH4-O2-NO in a gas-phase reaction was examined using a Cu-ZnO/SiO2 catalyst. Two types of Cu-ZnO/SiO2 catalysts were prepared with different compositions: 3:7:90 (denoted as CZS-1) and 5:5:90 (CZS-2) as the weight percent ratios of CuO:ZnO:SiO2. Both CH3OH and CH2O were observed as C1-oxygenates at 550 °C in the gas-phase selective oxidation of CH4 in CH4-O2-NO without a catalyst, but then only CH3OH was observed in the presence of the CZS-1, in addition to the direct gas-phase selective oxidation of methane. The catalyst temperature was 250 °C and the reaction pressure was 0.4 MPa. CH3OH, CO and CO2 selectivities increased and CH2O selectivity decreased in the presence of the Cu-ZnO/SiO2, in comparison to the values in the absence of the catalyst. We, therefore, suggested that three reactions: i.e. the hydrogenation reaction of CH2O, the dissociation reaction of CH2O, and the WGSR, progressed simultaneously on the Cu-ZnO/SiO2 catalyst in CH4-O2-NO.Since the selectivity of CH3OH did not vary during the variation of reaction temperatures from 150 °C up to 350 °C over the Cu-ZnO/SiO2 catalyst, we assumed that SiO2 was a favorable support to enhance the selectivity of CH3OH in a wider catalyst temperature region.